In "Proceedings Internal Conference on Acoustics, Speech, and Signal Processing (ICASSP), pp. 2578-2581, New York, April 1988, IEEE" is discussed a microphone array comprising four microphones positioned in the comers of a room with a square ground plan, whose microphone signals are processed so that the influence of noise signals superimposed on speech signals is reduced. For this purpose, the microphone signals are first mutually shifted with respect to time to cancel delay differences of a speaker with respect to the individual microphones. The microphone signals having thus in-phase speech components are superimposed on a sum signal by an adder device, so that the uncorrelated noise components of the microphone signals are diminished when superimposed. The diminishing is then not optimal if there is an inhomogeneous noise signal area. In that case different noise signal powers occur at the positions where the microphones are installed. The superimposed microphone signals are applied to an adaptive filter (Wiener filter) once they have been diminished by a correction factor used for taking the mean value. This filter is set by evaluating the in-phase microphone signals and provides a further suppression of the noise signals.